The present invention relates to the biomedical arts. It finds particular application in conjunction with cuff electrodes for stimulating nerves and will be described with particular reference thereto. It will be appreciated, however, that the present invention is also applicable to other types of implanted electrodes and biomedical devices.
Many types of nerve tissue damage do not heal. Such injuries leave a patient permanently without an appropriate nerve path for electrical signals or action potentials which travel from the brain to muscles or other biological tissue to cause a biological response. Similarly, such a discontinuity prevents action potentials from carrying sensory information or other biological feedback from the tissues to the brain. Moreover, there is also a tendency for action potentials to commence propagating naturally from below the injury site to the biological tissue causing an unconscious and unwanted biological response. Analogously, action potentials can propagate from above the injury site to the brain causing pain and erroneous sensory feedback.
Electrical potentials can be applied to nerve trunks and fibers to block the propagation of action potentials and for controllably initiating the propagation of action potentials in an upstream direction, a downstream direction, or both. Neural electrodes, such as illustrated in U.S. Pat. No. 4,602,624 to Naples, Sweeney, and Mortimer, and U.S. Pat. No. 5,324,322 to Grill, Jr., Creasey, Ksienski, Veraart and Mortimer controllably initiate and/or block action potentials in the nerves.
Although the prior art neural electrodes have proven effective, they do have drawbacks. Initially, certain types of prior art neural electrodes are labor intensive to manufacture, requiring the hand of a skilled fabricator to weld conducting wires to foil and fitting these foil conductors to silicone rubber coverings. Hand fabrication results in various problems, including the tendency of the foil conductors buckling when the metal-silicone structure is flexed. The flexure causes the foil to work harden and ultimately become a source for mechanical failure, stress corrosion, cracking and/or subsequent conduction failure.
Also, for neural electrodes whose patterns are formed with a metal deposition on a flexible substrate (e.g., silicone rubber or polyamide) there is a tendency for the metal to crack. The cracks on the surface appear as "cracked mud" at a microscopic level. Such cracks have the tendency to fill with uncured polymer when pressure is applied to a metal-polymer structure. This causes the uncontrolled formation of metal "islands," separated by the nonconducting polymer. Nonconducting polymer between "islands" eliminates electrical conduction along a trace by causing multiple open circuits.
The present invention provides a new and improved neural electrode and method of manufacture which overcomes the above-referenced problems and others.